The disclosure relates to the field of β-quartz glass-ceramics. More particularly it relates to tin-fined, darkened glass-ceramics of the lithium aluminosilicate type, containing a solid solution of β-quartz as the main crystalline phase, essentially free of As2O3 and of Sb2O3, articles comprising said glass-ceramics, and lithium aluminosilicate glasses as precursors of such glass-ceramics, as well as methods for forming said glass-ceramics and said articles.
With view to the toxicity of As2O3 and of increasingly strict regulations in effect, this toxic fining compound is desirably no longer used. For environmental considerations, it is also desired to no longer use Sb2O3 and not to use halogens, such as F and Br, which would have been able to replace at least partly said fining agents As2O3 and Sb2O3.
SnO2 has been proposed as a replacement fining agent. It is notably used when the precursor glass of the glass-ceramic (glass plate precursors of glass-ceramic plates, in fact) is obtained by floating. Indeed, applied with glasses containing As2O3 and/or Sb2O3 in their composition, such a floating method generates glass plates with a metal deposit at their surface (a metal deposit resulting from the reduction of As2O3 and/or Sb2O3).
The use of SnO2 as a fining agent however has two major drawbacks. It is less efficient than As2O3 (and, in absolute terms, it should therefore be used in a relatively large amount, which is not without posing any problems, more particularly of devitrification) and, as a more powerful reducing agent than As2O3 and Sb2O3, it is responsible for the appearance of an undesirable yellowish coloration during ceramming. This second drawback is of course a nuisance when it is sought to obtain transparent, essentially colorless glass-ceramics. This yellowish coloration results from Sn—Fe, Sn—Ti and Ti—Fe interactions, i.e., by way of charge transfer.
In view of the foregoing, it would be advantageous to provide colored glass-ceramic compositions that are substantially free of As2O3 and Sb2O3, and which possess desired optical properties particularly for their use in stove cook-tops.